Journal of Foot and Ankle Research 2012, 5:29
doi:10.1186/1757-1146-5-29

Published: 26 November 2012

Abstract

Background

Intrinsic foot muscle weakness has been implicated in a range of foot deformities
and disorders. However, to establish a relationship between intrinsic muscle weakness
and foot pathology, an objective measure of intrinsic muscle strength is needed. The
aim of this review was to provide an overview of the anatomy and role of intrinsic
foot muscles, implications of intrinsic weakness and evaluate the different methods
used to measure intrinsic foot muscle strength.

Method

Literature was sourced from database searches of MEDLINE, PubMed, SCOPUS, Cochrane
Library, PEDro and CINAHL up to June 2012.

Results

There is no widely accepted method of measuring intrinsic foot muscle strength. Methods
to estimate toe flexor muscle strength include the paper grip test, plantar pressure,
toe dynamometry, and the intrinsic positive test. Hand-held dynamometry has excellent
interrater and intrarater reliability and limits toe curling, which is an action hypothesised
to activate extrinsic toe flexor muscles. However, it is unclear whether any method
can actually isolate intrinsic muscle strength. Also most methods measure only toe
flexor strength and other actions such as toe extension and abduction have not been
adequately assessed. Indirect methods to investigate intrinsic muscle structure and
performance include CT, ultrasonography, MRI, EMG, and muscle biopsy. Indirect methods
often discriminate between intrinsic and extrinsic muscles, but lack the ability to
measure muscle force.

Conclusions

There are many challenges to accurately measure intrinsic muscle strength in isolation.
Most studies have measured toe flexor strength as a surrogate measure of intrinsic
muscle strength. Hand-held dynamometry appears to be a promising method of estimating
intrinsic muscle strength. However, the contribution of extrinsic muscles cannot be
excluded from toe flexor strength measurement. Future research should clarify the
relative contribution of intrinsic and extrinsic muscles during intrinsic foot muscle
strength testing.